Onset threshold of Raman scattering in a laser-irradiated plasma with short-wavelength density modulations

Abstract

The influence on stimulated Raman scattering of an ion-acoustic density modulation produced by stimulated Brillouin scattering is discussed, within the context of inertial confinement fusion. Via the density modulation, the Raman-driven electron plasma wave is coupled to multiple shorter wavelengths, which undergo an enhanced Landau damping. By numerically solving the modified dispersion relation of the electron plasma wave, in both kinetic and fluid frameworks, the competition between the coupling process and strong Landau damping is explored. Both convective and absolute growths are discussed: they appear to be strongly modified by a 10 % density modulation. An analytic fit is provided which well reproduces the numerical results of the convective stimulated Raman scattering.